1. Field of the Invention
The present invention relates to a novel pyridine derivative and its salt, a method for preparing the same, a herbicidal composition containing the same as an effective ingredient, and a method for killing weeds.
2. Discussion of Background
Heretofore, as a pyridine carboxylic acid derivative having a herbicidal activity, there were known 3-(4,6-dimethoxypyrimidin-2-yl)oxypicolinic acid derivative (Japanese Unexamined Patent Publication No. 84/1989), pyrimidyloxypicolinic acid derivative and pyrimidyloxyisonicotinic acid derivative (Japanese Unexamined Patent Publication No. 121973/1990 and 149567/1990).
However, these references do not describe a nicotinic acid derivative having a heterocyclic ring-containing substituent at the 2-position as in the compound of the present invention.
Heretofore, many herbicides have been developed, and have contributed to the saving of energy for the agricultural operations and to the improvement of the production efficiency. However, in their practical use, such herbicides have various problems. For example, a herbicide achieving a herbicidal effect specially at a low dose is desired in view of environmental problems. Particularly, a desirable herbicide should have a herbicidal effect for killing perennial weeds such as johnsongrass (Sorghum halepense) and purple nutsedge (Cyperus rotundus) which are widely distributed on agricultural lands throughout the world and are hardly killed. Furthermore, a herbicide having a satisfactory selectivity and safety to crop plants is particularly desired in respect of agricultural management.
Up to now, the known compounds as described in the above references do not always have satisfactory herbicidal effects.
The present inventors have conducted extensive research on nicotinic acid derivatives with an aim to develop a compound having a satisfactory herbicidal activity, and as a result, have found that the pyridine derivative of the present invention which is a nicotinic acid derivative having a heterocyclic ring-containing substituent at the 2-position, has an excellent herbicidal activity for killing annual and perennial weeds including gramineous weeds, cyperaceous weeds and broadleaf weeds by water treatment of rice fields and soil treatment or foliage treatment of upland fields, and also has a satisfactory safety to crop plants including rice, wheat and the like. The present invention has been accompanished on the basis of this discovery.